1. Field of the Invention
The present invention relates to triphenylamine derivatives and a method for preparing the derivatives. More specifically, the present invention relates to triphenylamine derivatives with low band gaps and high efficiency organic photovoltaic cells using the derivatives.
2. Description of the Related Art
The supply of fossil fuels as representative energy sources is finite and the emission of carbon dioxide from the combustion of fossil fuels brings about environmental problems, such as greenhouse effect. Under these circumstances, there is a growing demand for environmentally friendly alternative energy sources. In efforts to overcome the problems of fossil fuels, various energy sources, such as water power and wind power, are being investigated, and the sunlight is also investigated as a new renewable energy source due to its unlimited availability. Solar powered photovoltaic cells can be broadly classified into two groups: photovoltaic cells using inorganic materials, such as silicon, and photovoltaic cells using organic materials. In comparison with silicon-based inorganic photovoltaic cells, organic thin-film photovoltaic cells have the advantages of low fabrication costs and the possibility of manufacturing freely bendable, flexible, large-area devices. Due to these advantages, a great deal of research has been conducted on organic thin-film photovoltaic cells. Most studies on materials for organic thin-film photovoltaic cells have focused on polymeric materials (G. Li, V. Shrotriya, J. S. Huang, Y. Yao, T. Moriarty, K. Emery and Y. Yang, Nat. Mater., 2005, 4, 864-868, W. L. Ma, C. Y. Yang, X. Gong, K. Lee and A. J. Heeger, Adv. Fund'. Mater., 2005, 15, 1617-1622, H.-Y. Chen, J. Hou, S. Zhang, Y. Hang, G. Yang, G. Yang, Y. Yang, L. Yu, Y. Wu, G. Li, Nat. Photon., 2009, 3, 649). However, the control over the molecular weight of polymeric materials and the removal of catalysts are difficult. The efficiency of photovoltaic cell devices may vary depending on the arrangement of polymeric materials, resulting in poor reproducibility of performance. To overcome such drawbacks, there arises a need to develop a novel monomolecular compound that has a low band gap over a broad light-absorbing range, a high hole mobility and an appropriate molecular level, thus being suitable for use in the fabrication of a high efficiency organic photovoltaic cell.